This invention relates generally to an electrophotographic printing device, and more particularly a way of detecting the failure of a cleaning system used therein to remove particles adhering to the photoconductive member.
In the process of electrophotographic printing, a photoconductive surface is charged to a substantially uniform potential. The photoconductive surface is imagewise exposed to record an electrostatic latent image corresponding to the informational areas of an original document being reproduced. This records an electrostatic latent image on the photoconductive surface corresponding to the informational areas contained within the original document. Thereafter, a developer material is transported into contact with the electrostatic latent image. Toner particles are attracted from the carrier granules of the developer material onto the latent image. The resultant toner powder image is then transferred from the photoconductive surface to a sheet of support material and permanently affixed thereto.
This process is well known and useful for light lens copying from an original and printing applications from electronically generated or stored originals, and in ionography.
In a reproduction process of the type as described above, it is inevitable that some residual toner will remain on the photoconductive surface after the toner image has been transferred to the sheet of support material (e.g. paper). It has been found that with such a process that the forces holding some of the toner particles to the imaging surface are stronger than the transfer forces and, therefore, some of the particles remain on the surface after transfer of the toner image. In addition to the residual toner, other particles, such as paper debris (i.e. Kaolin, fibers, clay), additives and plastic, are left behind on the surface after image transfer. (Hereinafter, the term "residual particles" encompasses residual toner and other residual debris remaining after image transfer.) The residual particles adhere firmly to the surface and must be removed prior to the next printing cycle to avoid its interfering with recording a new latent image thereon.
Various methods and apparatus may be used for removing residual particles from the photoconductive imaging surface. Hereinbefore, a cleaning brush, a cleaning web, and a cleaning blade have been used. Both cleaning brushes and cleaning webs operate by wiping the surface so as to affect transfer of the residual particles from the imaging surface thereon. After prolonged usage, however, both of these types of cleaning devices become contaminated with toner and must be replaced. This requires discarding the dirty cleaning devices. In high-speed machines this practice has proven not only to be wasteful but also expensive. Blade cleaning involves a blade, normally made of a rubberlike material (e.g. polyurethane) which is scraped or wiped across the surface to remove the residual particles from the surface. Blade cleaning is a highly desirable method, compared to other methods, for removing residual particles due to its simple, inexpensive structure. However, there are certain deficiencies in blade cleaning, which are primarily a result of the frictional sealing contact that must occur between the blade and the surface. This frictional contact can cause blade failures such as creating a tear in the blade allowing toner to leak through the blade cleaner. This type of blade failure eventually causes copy quality defects that are large enough to detect on the copy.
The following disclosures may be relevant to various aspects of the present invention and may be briefly summarized as follows:
U.S. Pat. No. 3,918,809 to Hwa discloses an apparatus for cleaning liquid developer from upwardly moving support surface, such as reusable surfaces used for carrying latent electrostatic images. Cleaning blades are used to clean this surface. Separate support members hold the cleaning blades in contact with the surface being cleaned.
U.S. Pat. No. 5,034,774 to Higginson et al. discloses an apparatus for applying toner for developing an electrostatographic latent image formed on the charge retaining surface of a moving recording medium. The apparatus includes compliant cleaning blades disposed for contacting a drying roller to prevent agglomeration of paper fibers and toner particles on the interface between the roller and the scraper blade.